In general portable electronic devices such as electronic timepieces have used silver cells, mercury cells, etc. which serve as the power source. Such cells make the above mentioned timepieces operate during a predetermined period of time. However, such cells need to be exchanged regularly in order to provide continuous operation of the timepieces. This imposes on the users of such timepieces an economic burden since the cells are expensive.
It has been proposed to provide a small electric generating device for charging a secondary cell used as the power source of a portable electronic device such as an electronic timepiece. However, such generating device has had serious disadvantages. Among such disadvantages are an inability to produce a sufficiently high electromotive force to charge the secondary cell, high friction losses and poor endurance.